B-cell chronic lymphocytic leukaemia (CLL) is the most common form of leukaemia. To gain insight into the role of inherited factors in the disease, we have conducted a survey of the family histories of 268 CLL patients and have reviewed published familial cases and epidemiological studies. The results of our survey and published studies strongly support the hypothesis that a subset of the disease can be ascribed to a genetic predisposition. The most likely genetic model for inherited predisposition appears to be dominantly acting genes with pleiotropic effects because in many families CLL appears to be associated with other lymphoproliferative disorders.